I would actually love this. I use email for everything, it is so nice to have everything come to the same place. Right now I follow a few Mastodon users via an RSS-to-Email service, but the problem with that is that you can’t follow private accounts/see followers-only toots. It would be great to have a full email bridge.
I was considering making this myself at one point. But I think one of the big problem with ActivityPub is that it describes a single particular account. So if my ActivityPub-email bridge was running you wouldn’t also be able to access a Mastodon UI and for example browse other posts. So my account would need to be email-only which would be missing UX for a lot of things (like commenting on a random post I was linked to).